/*
 * Copyright (c) 2010 Peter Hayes
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.envconfig.util;

import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * Implements a hierarchy of configuration settings so that keys can
 * be overriden.
 *
 * @author Pete Hayes
 */
public class HierarchicalConfiguration extends AbstractConfiguration {
    // List of underlying configurations in descending order of precedence
    private List<Configuration> configurations;

    /**
     * Create a new instance of this class
     *
     * @param configurations The list of configuration objects in descending
     * order of precedence
     */
    public HierarchicalConfiguration(List<Configuration> configurations) {
        if (configurations == null) {
            throw new IllegalArgumentException("List of configurations must " +
                    "not be null");
        }

        this.configurations = configurations;
    }

    @Override
    public Set<String> keys() {
        Set<String> keys = new HashSet<String>();

        int size = configurations.size();
        for (int i=1; i<=size; i++) {
            keys.addAll(configurations.get(size - i).keys());
        }

        return keys;
    }

    @Override
    public String get(String key, String def) {
        for (Configuration configuration : configurations) {
            String value = configuration.get(key, null);

            if (value != null) {
                return value;
            }
        }
        return def;
    }
}
